A side wall system for a concrete casting mould, including a side part (1, 7) which is removably attachable to a casting bed by means of one or several magnets (11). The body (10) of the magnet part that carries the magnet (11) is provided with a gripping loop (14) or with a downwardly open gripping hook through which a release lever can be pushed in order to detach the magnet from the casting bed.